Sensitivity towards elevated pCO₂ in great scallop (Pecten maximus Lamarck) embryos and fed larvae

Abstract. The increasing amount of dissolved anthropogenic CO₂ has caused a drop in pH values in the open ocean known as ocean acidification. This change in seawater carbonate chemistry has been shown to have a negative effect on a number of marine organisms. Early life stages are the most vulnerable, and especially the organisms that produce calcified structures in the phylum Mollusca. Few studies have looked at effects on scallops, and this is the first study presented including fed larvae of the great scallop (Pecten maximus) followed until day 14 post-fertilization. Fertilized eggs from unexposed parents were exposed to three levels of pCO₂ using four replicate units: 465 (ambient), 768 and 1294 µatm, corresponding to pH_NIST of 7.94, 7.75 (−0.19 units) and 7.54 (−0.40 units), respectively. All of the observed parameters were negatively affected by elevated pCO₂: survival, larval development, shell growth and normal shell development. The latter was observed to be affected only 2 days after fertilization. Negative effects on the fed larvae at day 7 were similar to what was shown earlier for unfed P. maximus larvae. Growth rate in the group at 768 µatm seemed to decline after day 7, indicating that the ability to overcome the environmental change at moderately elevated pCO₂ was lost over time. The present study shows that food availability does not decrease the sensitivity to elevated pCO₂ in P. maximus larvae. Unless genetic adaptation and acclimatization counteract the negative effects of long term elevated pCO₂, recruitment in populations of P. maximus will most likely be negatively affected by the projected drop of 0.06–0.32 units in pH within year 2100.